Follow up Autoresponder PRO :: Few things to note on the script performance:

• Your Host restrictions: If you are on shared hosting, certainly there is some host restrictions to run big lists, especially if you are doing large list importing and mass mailings. This type of script activity is considered as spam by hosts. If you are using the script in regular way like setting up subscription form on your websites allowing your list to grow, you will be on safe side of the edge. Solution: If you are doing mass mailings or big lists, go for your dedicated server or VPS.
• Certain hosts: If your website is hosted by hosts like Yahoo.com, ipowerweb.com, please check with your host before buying the script. We won't guarantee that script will work on your host servers.

 Follow up Autoresponder PRO :: How it tracks the email link clicking and its limitations:

• Who opened the emails
• Who clicked on the links in emails

• This 'who opened emails' feature ONLY works with HTML messages. But click tacking can be used for both text and html messages.
• People installs software that blocks the referer. So script can't tell the referer.
• People disable javascript and image display in their browsers. So script can't tell who opened the email.
• If people copy and paste the url in the browser, then script can't tell the referer.
• People with firewalls.